A press-formed article can be obtained by placing a blank in a die provided with a concave part and drawing the convex part of a punch into the concave part. At this time, when the edges of the blank are held down by a blank holder, a neat formed article can be obtained that is free of wrinkles. However, rather than simply holding down the edges of the blank, it is preferable to adjust the restraining force in accordance with the progress of the press, i.e., the degree of progress of the draw process.
A press apparatus capable of adjusting the restraining force has been proposed in the past, e.g., in Japanese Patent Application Laying-Open Publication No. 9-29349 (JP 09-29349 A). The proposed press apparatus is described using FIG. 9 hereof.
As shown in FIG. 9, in the press apparatus described in JP 09-29349, the occurrence of fractures 120 in the raw material 111 is prevented by effecting variable point beads 105 in a point shape at the appropriate sites during an arbitrary portion of the forming period.
Fixing beads 103 are also provided to the outside of the variable point beads 105. When the fixing beads 103 are provided to the outside, the amount of cut material increases, and the yield is poor when the edges of the formed article are cut off after forming.
The blank is also drawn in towards the center in conjunction with pressing while being subjected to the restraining action of the fixing beads 103. Since the fixing beads are on the outside, a large distance occurs between the fixing beads 103 and the forming part. The larger this distance, the more likely it is that wrinkling will occur along the distance, and the wrinkle-preventing effects of the fixing beads 103 are diminished.
Furthermore, since the variable point beads 105 are provided more towards the inside than the fixing beads 103, the movement mechanism for moving the variable point beads 105 is disposed to the inside of the fixing beads 103. However, the space to the inside of the fixing beads 103 is limited, and the movement mechanism is therefore subject to space limitation, and unavoidably has a complex structure. A complex movement mechanism is not preferred, because the cost of the press apparatus increases.
Specifically, the press apparatus of JP 09-29349 A has drawbacks with respect to yield rate, wrinkling, and structure, and there is a need for a press forming die that has a good yield rate, no occurrence of wrinkling, and a simple structure.